Drilling fluids, also commonly referred to as drilling mud or drilling muds, have been used for many years and provide a number of benefits for drilling. Drilling fluids are directed through the hollow axis of the drillstring to lubricate and cool the drill bit at the bottom of the well. The drilling fluids return to the surface in the annulus between the drillstring and the interior wall of the drillstring carrying drill cuttings (rocks, sand, shale, grit and other debris) back to the surface. At the surface, drilling fluids are processed to remove drill cuttings and undesirable drill solids, then recirculated into the well. Another function of the drilling fluids is attained by the addition of loss circulation materials sometimes referred to by the letters “LCM” or loss prevention materials, also referred by the letters “LPM”. The function of the LCM is to seal porous and permeable or naturally fractured formations and to arrest hydraulic fracturing of formations, preventing the drilling mud from leaking away from the wellbore which is a condition called “lost circulation”. The function of the LPM is to prevent or significantly limit hydraulic fracturing of the formation to the near wellbore region to create a stronger wellbore, this application of LPM is referred to as wellbore strengthening which prevents the drilling mud from leaking away from the wellbore. It should be noted that LCM/LPM does not dissolve or react with the drilling mud and generally comprises solid granular, fibrous, or flake-like materials that are able to form plugs by the accumulation of many individual LCM/LPM particles. Wellbore strengthening and lost circulation remedies using LCM/LPM may not be fully utilized because it is impractical to recover and recycle the materials used to in these operations and also to process the drilling fluid to remove the drill cuttings and undesirable drill solids. Typically, screening operations may be bypassed to retain the wellbore strengthening and lost circulation materials for a period of time such that normal processing to remove drill cuttings and undesirable drill solids cannot be utilized or the LCM/LPM is used for only a single pass through the well then removed and discarded at the surface.
In addition to the functions described above, drilling fluids also often include other materials, sometimes called “weighting agents” that alter the density of the mud and most commonly increase the density of the drilling mud to maintain substantial head pressure in the wellbore. Maintaining substantial head pressure is also called “well control” and well control basically means drilling and completing the well while maintaining head pressure that avoids a “blowout” or “kick”. A blow out or kick primarily occurs when the pressure exerted on the walls of the wellbore becomes less than the pressure a fluid in a high pressure formation that has been penetrated by the wellbore. Blow outs and kicks are very dangerous and destructive. Weighting agents are finely ground materials which make the removal of fine drill solids by processing equipment such as hydrocyclones and rotating centrifuges considerably less efficient. Often both well control and lost circulation control are needed in the same interval such that drilling fluids have both a weighting agent and loss circulation materials to maintain a substantial volume of dense drilling fluid in the wellbore at all times.
In conventional drilling operations, the drilling fluids are recirculated after being processed to remove the drill cuttings and other undesirable solids from the fluid. Typically, the separation of larger drill cuttings is done based on size with a screened shale shaker and smaller solids may be partially removed by additional processing equipment such as hydrocyclones or rotating centrifuges which work based on the mass of a particle. As the LCM/LPM materials and weighting agents are solids, they interfere with the efficient removal of drill cuttings and other undesirable solids because the particles have similar size or mass. Since such materials have not been very expensive, there has been little incentive to consider ways to recover or recycle these materials. However, advances in wellbore strengthening technology, improved LPM materials and an increasingly limited supply of quality weighting materials has created the need for improved methods for the recovery and recycling for drilling fluids materials. At the same time, petroleum drilling operations in remote areas makes disposable materials more expensive when one considers the logistical costs of shipping such materials and maintaining large inventories of the same, particular in offshore or small worksite locations.